Tuned signal detector for use with a radio frequency receiver

ABSTRACT

Disclosed is a tuned channel detector which includes a cable path between a radio frequency source and a receiver such as a TV, wherein the radio frequency source passes first through an attenuator and second through a signal selection module comprising two opposing directional couplers and a single-pole/double-throw switch. The channel to which the TV is tuned is determined by measuring the TV&#39;s local oscillator signal from the cable which feeds the radio frequency signal to the TV and, additionally or alternatively, by comparing the signal strength of the input and reflected TV carrier signals at and around the channels under test. Signal detection is further enhanced by modulating the signal mixed with the local oscillator with a tone and/or testing only during certain intervals such as the vertical synchronization interval or the power line cycle. A tone detector having a synchronous rectifier is used to detect low level local oscillator signals. Tuned channel detection is further enhanced through the use of artificial intelligence techniques.

This is a continuation of application Ser. No. 08/098,223, filed Jul.27, 1993, now U.S. Pat. No. 5,404,161 issued Apr. 5, 1995.

BACKGROUND OF THE INVENTION

The present invention relates to tuned channel detection systems and,more particularly, to television signal detection methods and apparatusfor determining the channel to which a television receiver is tuned.

For marketing research, program ratings, consumer surveys, and the like,it is often advantageous to determine the channels to which thetelevisions within a given viewing area are tuned. The motivation anddesire for collecting such information is well-known and thus, furtherelaboration is unnecessary.

Conventional methods for determining the channel to which a television(TV) receiver is tuned involve the detection of the TV's localoscillator signal. The detection of the local oscillator signal in andof itself is old and well-known in the art. The prior art illustratesvarious apparatus, both invasive and non-invasive to the televisionreceiver circuitry, which have been used as attempts to provide channeldetection means which are more robust and less susceptible to a falsereading. Enhanced methods are also used in the detection of the TV'slocal oscillator signal. Non-invasive methods have typically used anantenna tuned to the TV's local oscillator signal, thus no directphysical connection is made to the television. Invasive techniques, onthe other hand, typically use a probe to a circuit point within a TV'stuner circuitry or within a set top cable converter box which providesthe detector apparatus with a direct connection to the tuner, thusallowing for both the injection and measurement of signals at the tuneror set top converter. While a direct connection makes it easier todetect the local oscillator signal, it is obviously more desirable touse more non-invasive approaches.

Some examples of non-invasive methods for improving the integrity oflocal oscillator signal detection include such systems as thosedisclosed in U.S. Pat. No. 4,723,302 issued Feb. 2, 1988 to Fulmer, etal.; U.S. Pat. No. 3,312,900 issued Apr. 4, 1967 to Jaffe; and U.S. Pat.No. 4,577,220 to Laxton, et al.

Fulmer, et al. describe detecting the local oscillator signal of the TVand storing characteristic values of the signal for the fundamental anda plurality of harmonic frequencies of the local oscillator signalswhich correspond to predetermined channels. The local oscillator signalfundamental frequency and the corresponding harmonic frequencies whichare observed are compared to the stored values to identify the tunedchannel. The Fulmer system uses an antenna tuned to the local oscillatoror, in the alternative, a direct connection to the radio frequency (RF)input cable signal path.

The Jaffe and Laxton systems both use an antenna tuned to the localoscillator signal and placed in the vicinity of the tuner circuitry ofthe TV set. Since signals from the television line scanning circuitrytend to modulate the local oscillator signal, the Jaffe system extractsthe line scanning information from the local oscillator signal toidentify the tuned channel. The Laxton system uses a closed looparrangement to "lock on" the frequency of the detected local oscillatorsignal.

Notwithstanding the methods and apparatus described thus far, tunedchannel detection through the determination of a TV receiver's localoscillator signal frequency remains problematic. The tuners used by thevarious manufacturers of TVs, video cassette recorders (VCRs) and cableconverter boxes (set top converters) naturally have varyingcharacteristics thus making the positioning of an antenna appropriatelyin the vicinity of the tuner problematic. Moreover, the frequency of thelocal oscillator signals generated within TVs, VCRs, and set topconverters will range, depending upon the tuned channel, from about 100MHz to 1400 MHz which in and of itself makes detection a considerabletask. In any case, the local oscillator signal's location will only beknown approximately, and typically it will be a very low level signalburied down in the noise. It may also be difficult to discern localoscillator from the color carrier when they are in close proximity.These factors along with signal interference from other sources make itdesirable to provide a tuned channel detection means having greaterintegrity than that provided by today's systems. To this end, betternon-invasive methods for detecting and/or verifying the tuned channelincluding improved methods of detecting local oscillator signals aredesirable.

SUMMARY OF THE INVENTION

Given the difficulties surrounding the initial detection of localoscillator emanating from a TV and then the difficulty in discerningthat signal from other signals and background noise, the presentinvention focuses upon ensuring that the process of tuned channeldetection has sufficient integrity by providing not only enhancedmethods for detecting the local oscillator signal, but also completelyindependent means for detecting the channel to which the receiver istuned. The enhanced techniques used by the present invention for localoscillator detection include: (1) mixing the signal tuned by the localoscillator detection tuner with a frequency modulated (FM) signal of themixer wherein the modulated signal is that of a tone which may be FMdetected and filtered to detect and measure the presence of the TV'slocal oscillator signal in the presence of high levels of noise; (2)sampling for the measurement of the local oscillator signal only duringthe vertical synchronization interval (vertical blanking period) duringwhich there is no color carrier present, thus alleviating difficultiesassociated with discerning the local oscillator from color carriersignals; (3) pulse timing of the vertical synchronization intervalinformation for scrambled channels at a central control computer andconveying such timing information to the remote channel detectors forvertical synchronization interval sampling; and (4) detecting a 60 Hzmodulated signal and then sampling for the detection of the localoscillator only at the same point in the power line 60 Hz modulationcycle, thus alleviating the difficulties of detecting the localoscillator signal when it has been modulated by the 60 Hz power line.

Tuned channel detection in accordance with the embodiment may also beperformed in response to reflected signals at the radio frequency inputof the TV. The signal tuned by a TV exhibits low impedance to the tunedsignal at the TV radio frequency input thus resulting in a high returnloss ratio, whereas signals not tuned by the TV exhibit low return lossratios because a majority of their signal energies are reflected backfrom the TV, because of the high impedance mismatch for non-tunedsignals. The differing return loss ratios can be used to identify theparticular channel to which the TV is tuned. The return loss computationis a highly reliable method in and of itself for determining the channelto which the TV is tuned. An advantage of using return loss ratios isthat the TV carrier signals being measured are high level signals whosefrequency is known substantially exactly. Accordingly, since the returnloss computation method is independent of the local oscillator detectionmethod, the two methods may be used together resulting in an extremelyrobust system for tuned channel detection wherein the possibility for afalse detection is very remote.

A tuned channel detector in accordance with the embodiment includes asignal path between a radio frequency input and a TV, wherein the radiofrequency input passes through a signal selection module comprising twoopposing directional couplers and a single-pole/double-throw switch. Theradio frequency input may be any radio frequency signal source,including an antenna, a satellite dish, or a cable input from a cabletelevision (CATV) system. The TV receiver as contemplated hereinincludes not only TVs, but also VCRs and set top converters or with anysystem having a local oscillator for tuning the front end of a receiver.

The directional couplers are transmission coupling devices for passingeither the forward or backward (reflected) signal in a signal path. Asdescribed, an embodiment of the signal selection module has two opposingdirectional couplers such that both the forward and the backward signalsare separately passed. The switch is used to select between the forwardand backward signals. The ability to select between forward and backwardTV signals is used both for local oscillator detection and the returnloss computation. For local oscillator detection, the backward signalprovides a source of local oscillator signals leaking back from the TVonto the input signal path, and forward signal selection provides thelocal oscillator detector with the TV carrier signal both forcalibration of the detector and for detection of the verticalsynchronization intervals. Within the return loss computation the signalselection module provides separate measurement of the incoming (forward)and the reflected (backward) signals.

Alternative embodiments tailored particularly for use with set topconverters may use alternative forward and backward signal selectionmodules because local oscillator signals generated within suchconverters are at frequencies significantly higher than those generatedwithin a TV or conveyed on the radio frequency signal path. It may alsobe advantageous to equip a signal selection module intended for use witha set top converter with a block converter between the module'scrossover network and switch which shifts the spectrum to the televisionband.

The channel detector includes a tuner for reception of forward andbackward signals and an intermediate frequency (IF) filter narrows thesignals from the tuner to a particular frequency range. The resultingsignal is then mixed with a signal from a voltage controlled oscillator(VCO) and presented to a narrow band-pass filter allowing detection byan amplitude modulation (AM) detector. This circuitry is used both forthe detection of local oscillator and for the detection of incoming andreflected TV signals for the return loss ratio computation. The outputof the VCO may also be modulated with a tone which is then detected by afrequency modulation (FM) detector to aid in local oscillator detection.To this end, a tone detector having a synchronous rectifier is used todetect low level continuous wave (CW) signals (herein the localoscillator signal).

In the present tuned channel detector, the channel to which a televisionreceiver is tuned is thus determined by measuring the receiver's localoscillator signal from the signal path which feeds the radio frequencysignal to the TV and, additionally or alternatively, by comparing thesignal strength of the input and reflected TV carrier signals at andaround the particular channel under test (return loss ratios). Theability to detect the local oscillator signal is further enhanced bymodulating the signal mixed with the local oscillator with a tone andtesting only during certain intervals such as the verticalsynchronization interval or the power line cycle. It may be furtheradvantageous to conduct the return loss computation only duringparticular sampling intervals as well. The integrity of the tunedchannel detection is still further enhanced through the use ofartificial intelligence techniques.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram of a tuned channel detector connected to atelevision;

FIG. 2 is a more detailed block diagram relating to the controller usedwith the tuned channel detector;

FIG. 3 is a combined block diagram and schematic diagram of a portion ofthe tuned channel detector;

FIG. 4 is a combined block and schematic diagram illustrating animplementation of the signal mixing, filtering and AM/FM detectionreceiver;

FIGS. 5A, 5B, and 5C represent tabular data illustrating theeffectiveness of the return loss computation;

FIGS. 6A and 6B are block diagrams illustrating the scrambled channelsampling aspect of the present invention wherein FIG. 6A representsvertical synchronization interval detection and "time stamp" circuitrywithin the central control computer; and wherein FIG. 6B representscircuitry in a channel detector for the reception and utilization of"time stamp" information with a phase lock loop circuit;

FIG. 7 illustrates a signal selection module for use by a tuned channeldetector with a set top converter;

FIG. 8 is a schematic diagram of a signal selection module for use witha set top converter; and

FIG. 9 is a program flow chart for table-driven software which usesprogrammable channel detection table entries for channel detection dataand parameters in accordance with the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 1 is a block diagram showing a tuned channel detector connected toa TV 102, which represents the user's TV under test. TV 102 is used bythe viewer to tune in TV signals received from a radio frequency source108. As illustrated, radio frequency source 108 is a TV antenna butother radio frequency sources are contemplated. Such additional radiofrequency sources include satellite dishes and cable TV inputs. Radiofrequency source 108 is coupled to an attenuator 106 by a communicationpath 116, and the output of attenuator 106 is coupled to a signalselection module 104 via a communication path 114. A communication path110 couples the radio frequency signals from the signal selection module104 to the TV 102.

The signal selection module 104 comprises two opposing directionalcouplers 120 and 122 and a single-pole/double-throw switch 124. Aportion of signals reflected or radiated from receiver 102 oncommunication path 110 are coupled by directional coupler 120 andpresented to a pole "A" of switch 124 via path 126. A portion of inputsignals from radio frequency source 108 are coupled by directionalcoupler 122 to pole "B" of switch 124 through path 128. Switch 124 isused to connect either the signal on path 126 or path 128 to a detectortuner 130 of the channel detector apparatus via path 112.

The detector tuner 130 is a TV tuner which actually comprises its ownlocal oscillator, a mixer, and an output filter (not shown). Thedetector tuner 130 is used to select portions of television signals onpath 112 for analysis by later circuitry as is described in detail laterherein. The output bandwidth of detector tuner 130 is typically about 6MHz from about 41 MHz to 47 MHz. One such tuner is Phillips model UV936,which covers the spectrum from about 50 to about 800 MHz.

Detector tuner 130 presents selected radio frequency signals at anintermediate frequency of 44 MHz. The output of detector tuner 130 isfurther filtered by an IF filter 132 which has a bandwidth ofapproximately 1 MHz with cutoff frequencies at about 43.5 and about 44.5MHz. The passband of IF filter 132 thus passes the signals selected bydetector tuner 130 as an intermediate frequency signal at 44 MHz.

The output of IF filter 132 is applied to a signal path 135 and isamplified by an IF amplifier 133. In one embodiment, a Motorola MC 1350video amplifier was used as IF amplifier 133. The resulting signal andthe output of a voltage controlled oscillator (VCO) 134 are then mixedin a mixer 136. The output signals of mixer 136 are connected to a verynarrow band-pass filter 138 (e.g., a 10.7 MHz bandpass crystal filterhaving a 15 KHz bandwidth), which in turn presents its output to an AMdetector 140 and a FM tone detector 142. While the bandpass filter 138used in the preferred embodiment is a 10.7 MHz crystal filter, othertypes of filters at other frequencies may also be practical for usewithin alternative embodiments. Taken together VCO 134, mixer 136,band-pass filter 138, AM detector 140 and FM tone detector 142 representan AM and FM fine tuning receiver which is enclosed by a dashed boxlabeled 260.

A controller 200 is used to control the apparatus. The controller 200could be a human operator, but in the present example is amicroprocessor controlled computing arrangement as discussed below.Various control paths are used by the controller 200 to control theapparatus. A switch control path 125 allows the controller to change theposition of the switch 124 between its "A" and "B" positions to selectsignals either from the source 108 or the TV 102 for presentation onpath 112. A gain control path 212 and a data control path 214 controlthe detector tuner 130 to select the particular frequency bands from thesignals on path 112 and regulate the amplitude of the selected signals.A control path 216 controls the gain of the IF amplifier 133, and asignal on control path 251 controls the output of VCO 134. Thecontroller 200 also receives input signals from an AM detect signal path141 and a FM detect signal path 143 which are used as described below.

It should be appreciated that the apparatus described herein selectsfrom the input radio frequency signal path which feeds radio frequencysignals to the TV 102 thus providing access to various input radiofrequency signals as well as reflected and leaked signals propagatingbackwards from the TV 102 along the input signal path. The apparatus ofFIG. 1 is used to detect and measure incoming and reflected TV picturecarrier signals and to detect and measure the local oscillator signalsleaking out from the TV 102. Such detected and measured signals are usedto identify which of a plurality of television channels the TV 102 istuned.

The TV 102 includes a local oscillator (not shown) which generates asignal having a selected one of a plurality of frequencies necessary toproduce a 45.75 MHz intermediate frequency signal representation of atuned channel signal within TV102. The particular television localoscillator frequency needed by the TV 102 to receive each televisionchannel is substantially the same from receiver to receiver andwell-known. Since a portion of this local oscillator signal leaks outonto the input path 110, the local oscillator signal's frequency may bedetected for the purpose of determining the channel to which the TV 102is tuned. The local oscillator leakage signal can be quite small and maybe buried in a high level of noise and/or TV carrier and sidebandsignals. The embodiment may be reliably used to detect a televisionlocal oscillator signal even when the local oscillator leakage signallevel is well below the noise level. Moreover, as will be appreciated bythose skilled in the art, the above may also be used to detect any lowlevel continuous wave (CW) signal in high noise levels.

To perform local oscillator detection, the controller 200 puts theswitch 124 in its "A" position to select backward propagating signalsfrom TV 102. It is advantageous to attenuate the radio frequency sourcesignal delivered to the TV 102 to a level no larger than necessary toreceive a clear picture so that the local oscillator signal from the TV102 is not completely masked. By attenuating the source signal, one canfind the frequency location of a very low level local oscillator signalwhich might otherwise be lost in the source signal and its reflection.Attenuator 106 is provided for this purpose, and it may be fixed,switchable or variable via control path 107.

The controller 200 implements local oscillator detection of signals onpath 112 by stepping the selection performed by detector tuner 130 fromone expected local oscillator frequency to another until a localoscillator signal is detected at the output of the detector tuner 130.The controller 200 controls the detector tuner 130 to nominally place anexpected local oscillator frequency at about 44 MHz and the selectedsignal is connected to mixer 136 via the filter 132 and IF amplifier133. Controller 200 then controls VCO to apply a signal to mixer 136having a frequency which will center the expected frequency fromdetector tuner 130 in the passband of band-pass filter 138.

Local oscillator signals, although generally known, can vary dependingupon the particular TV 102 under test. In order to cover the range ofpossible signals, the VCO 134 is presented by controller 200 with asweep voltage at its input which causes a sweep of frequencies from theVCO 134 to allow for some deviation of the local oscillator signals fromtheir nominal 44 MHz while still providing for accurate detection withinthe swept frequency range. Frequency sweeping also allows for fairlywide tolerances in the design of the mixer 136. Since the expected localoscillator signal is received at approximately 44 MHz, the frequenciesfrom the VCO 134 necessary to drive a 10.7 MHz output at mixer 136comprise a frequency sweep in the vicinity of 33.3 MHz.

There are five (5) possible modes of local oscillator testing which maybe used by the tuned channel detector apparatus. The modes of localoscillator testing, in order of increasing testing time, are: (1)amplitude testing; (2) tone testing; (3) sampling testing; (4) linesynchronization sampling; and (5) scrambled channel sampling.Advantageously, the testing modes may be used individually or incombination.

When using amplitude testing to detect local oscillator, the controller200 tunes detector tuner 130 to the proper frequency, provides theappropriate VCO 134 output signals, and searches a narrow spectrum atthe output of band-pass filter 138 for a signal at the appropriate localoscillator frequency. The AM detector 140 is used to detect a signalwhich matches the expected local oscillator signal to within somepredetermined tolerance of amplitude and frequency.

Tone test is used if the amplitude of the local oscillator is so lowthat it cannot be reliably differentiated from the reflected "noise" bythe AM detector 140. Tone detection is performed by FM modulating thesignal generated at VCO 134 prior to mixing that signal with theincoming signal from detector tuner 130 at mixer 136. Using acombination of audio filters and a synchronous tone detector, a localoscillator signal can be reliably detected even in the presence ofsignificant noise. This is so because an FM signal, when mixed withnoise, will produce more noise. However, the presence of a continuouswave local oscillator signal even buried deep below the noise level,will result in a tone which, with proper filtering, can be detected.Controller 200 generates the tone used for the FM modulation by varyingthe VCO 134 control signal on conductor 251. When the FM modulatedsignal from VCO 134 is mixed at mixer 136 with an incoming expectedlocal oscillator signal, an FM modulated 10.7 MHz signal will result.The FM tone detector 142 is used to detect the tone in the 10.7 MHzsignal.

The sampling test may be used with either the amplitude or tone modes oftesting. Sampling is used because the local oscillator signal requiredto tune the majority of TV channel signals lies in the vicinity of thecolor carrier signal of the channel which lies seven (7) channels abovethe channel in question. Of course, when no TV channel exists sevenchannels above the channel in question, then interference is not anissue. In theory, the color carrier of the interfering channel will be170 KHz away from the expected local oscillator signal of the channel inquestion. However, while amplitude detection should be adequate if thelocal oscillator signal level is larger than the reflected colorcarrier, due to real world tolerances the local oscillator could beconfused with the color carrier or its sidebands if the local oscillatorsignal level is smaller than the color carrier. In order to avoidpossible confusion between an expected local oscillator signal and apossibly interfering color carrier signal, the expected local oscillatorsignal can be sampled during the vertical retrace interval of thepossibly interfering channel (vertical blanking) when the color carrieris not present. Thus, if one looks for local oscillator only during thevertical retrace interval of the interfering channel, typically sevenchannels above the channel in question, then the local oscillator signalof the channel in question cannot be confused with the color carrier ofthe interfering channel. The vertical synchronization or retraceinterval is only about 1.2 milliseconds, thus it takes successivesamples using a sample-and-hold technique and signal integration to geta reliable reading. Hence, it takes longer to get a reading withvertical synchronization interval sample than with the methods oftesting discussed thus far, but vertical synchronization intervaltesting is no less reliable.

With the switch in position "B" and the detector tuner 130 tuned to theinterfering channel (where the local oscillator of the channel inquestion would lie), the proper vertical synchronization interval can beextracted to determine the correct sampling interval corresponding tothe vertical synchronization interval. A video detector 252 is providedto convert the non-baseband output of IF filter 132 via signal path 135to composite video which is then presented to vertical synchronizationinterval detector 254 which provides vertical synchronization intervalinformation to controller 200. The controller 200 uses verticalsynchronization interval detector 254 to determine the verticalsynchronization interval rate and then software is used to generate a"pseudo-sync" for use during the sampling mode. Video is turned off(switch 124 position changed to "B") after "pseudo-sync" is established.

Occasionally the local oscillator of a TV 102 will be modulated by the60 Hz power line signal to such an extent that the local oscillator will"sweep" through a narrow band of frequency and thus a steady levelcannot be maintained for measurement. The presence of the 60 Hzmodulation of a local oscillator signal may be detected by thecontroller 200 from signals on path 141 at the output port of AMdetector 140. Once detected, the 60 Hz synchronization sampling methodmay be used by determining the 60 Hz synchronization from a 60 Hzsynchronization detector 258 connected to a 60 Hz power source 256. 60Hz sampling can be used to sample the modulated local oscillator signalat the same location in its "sweep," and then integrate the resultssimilarly as previously described for vertical synchronization intervalsampling using sample-and-hold and signal integration techniques.

The 60 Hz and vertical synchronization interval signals (the "sampling"test methods) are used for performing sampled tuned channel detectionmethods only during the 60 Hz and vertical synchronization intervalsample periods. When no local oscillator signal is detected at anexpected frequency, the controller 200 re-tunes the detector tuner 130to select a new expected local oscillator signal and the above tests areagain performed.

The present embodiment may also be used to detect a tuned channel bydetermining the return loss in reflected television signals. Since areceiver exhibits matched impedance to a tuned signal while exhibitingmismatched impedance to signals not tuned at the radio frequency input,the result is high return loss for tuned signals and low return loss fornon-tuned signals, because a majority of their energies are reflectedback from the receiver due to the high impedance mismatch for non-tunedsignals. Differing return loss ratios are thus used to identify theparticular channel to which the TV 102 is tuned, as will now bedescribed.

The expected return loss of each tuned channel can be used in a returnloss tuned channel detection method to identify the tuned channel of areceiver. Prior to performing tuned channel detection using the returnloss method, a profile of the return loss characteristics of a receiveris created and stored in controller 200. At its very simplest, thereturn loss profile would consist of a value representing the reflectedpicture carrier signal strength measurement for each possible tunedchannel. (Other components of the television signal might also be used.)

The tuned channel detection method then successively tunes detectortuner 130 to select the picture carrier of possible tuned channels andcompares the measured reflected picture carrier signal strength valuewith the stored profile. When the measured value matches a value storedin the profile of controller 200, a likely tuned channel has beenidentified.

More complex expected signal profiles, as discussed below, may beproduced and stored to improve the certainty of channel detection.Further, such profiles may be stored in controller 200 duringmanufacture or the profile may be learned by the tuned channel detectorduring setup operations when the channel detector apparatus is firstconnected to TV 102. In the latter "learning" case, an operator orautomated equipment would tune the TV 102 to successive channels andallow the detector apparatus to measure and store the necessary valuesat each tuned channel to create the profile.

To prepare a profile, attributes are determined for the measureddifferences between the forward and backward signal strengths for one ormore picture carrier signals at and adjacent to the channel beingtested. The controller 200 accomplishes this by placing switch 124 inposition "A" for backward signal selection and position "B" for forwardsignal selection. By comparing the forward signals with the backwardsignals, a coefficient which can be stored as an "attribute" for theparticular signal is computed for later channel identification. Onceattributes are determined for a particular channel, the TV 102 channelis changed to the next channel and the controller 200, having beennotified that the next channel is tuned, then determines the attributesfor the next channel as described. Once stepping through all channelsand once the controller 200 has attributes for all channels, then thecontroller 200 compiles a TV profile from the channel attributes. FIGS.5A, 5B, and 5C represent values accumulated in preparing such a profile.

In FIGS. 5A, 5B and 5C, the data illustrated in tabular form wasobtained with a tuned channel detector by measuring the differencebetween the incoming picture carriers and their reflection (in db) fromthe TV 102 receiver (herein Sylvania Model #19C 518). The TV 102 wastuned to channel 25 through channel 35, and then the signal reflectionswere measured for the tuned channel and the two adjacent upper and lowerchannels. This data would be "learned" by the system and would becomethe "attributes" of the TV 102 under test. The data collected are shownin part in FIG. 5A.

With the "learned" profile generated for all channels, the controller200 may test channels sequentially by measuring the profiles for allchannels being tested by looking for a match with the profiles in the"learned" table for all channels; if the profiles do not match for anindividual channel, then the next channel in sequence is tried. A"figure of merit" is determined for differences between learned andmeasured values. The channel having the lowest "figure of merit" ispicked as the tuned channel. Once the measured profile matches thelearned profile, the tuned signal is detected.

Measuring the detection of one or more adjacent signals will improve thechances of a correct detection in accordance with this method. It hasbeen determined that reliable channel detection may be performed usingreturn loss where only one or two adjacent signals are measured inaddition to the signal under test. This is done, for example, bymeasuring the two lower adjacent signals, the two upper adjacent signalsand the signal being tested (five signals in total). Note that"adjacent" signal means adjacent in signal frequency and not necessarilyin channel number. Thus, Channel 13 is adjacent to Channel 23, not 14,as is understood by those skilled in the art.

Return loss testing may also be used with either the 60 Hz or verticalsynchronization sampling modes. In fact, since a constant picturecarrier signal ensures more accurate return loss ratios, it is desirableto use vertical synchronization sampling while computing return lossratios. In this regard, it should be noted that vertical synchronizationsampling is actually different when done for return loss than when donefor local oscillator testing. In particular, with return loss testing,the vertical synchronization is derived from the channel being testedrather than some interfering channel. Since the channel picture carrieritself, as opposed to the corresponding local oscillator, is the signalwhich is being tested, there is no interfering channel. The sampling isused to ensure fairly constant picture carrier measurements because nopicture level information is present during vertical retrace.

FIG. 2 illustrates controller 200 which includes a microprocessor 202.Microprocessor (μP) 202 is connected to the basic apparatus of the tunedchannel detector for controlling various portions thereof. The SIGNETICS80C552 microcontroller has been used in the preferred embodiment asmicroprocessor 202. A detailed description of the instruction set,interfacing requirements, etc., can be found in the SIGNETICS (Phillips)Data Book "80C51-based 8-bit microcontrollers." The microprocessor 202is, of course, associated with read only memory (ROM) and random accessmemory (RAM) components and appropriate interface circuitry (not shown),all of which may be incorporated within microprocessor 202.

The microprocessor 202 is connected to an optional terminal 218 whichmay be used for manual operation of the detector at a remote locationprimarily for testing the apparatus and for controlling manual learning.Optionally, controller 200 may include an LED numeric display 220 whichprovides an indication representing the channel to which the TV 102 istuned, and various colored lamps 222 which indicate apparatus' mode andoperating conditions.

A data path 204 connects microprocessor 202 with a central controlcomputer 206. Generally, the public telephone network and modems areused for data path 204 between microprocessor 202 and central controlcomputer 206. Industry standard RS-232 communication protocols andcircuitry are provided to interface the microprocessor 202 to theterminal 218 and data path 204. Dedicated RS-232 driver/receiver chipsare readily available for this purpose. Input and output (I/O) ports areavailable on the microprocessor 202 for sending and receiving data toand from various portions of the subject channel detector apparatus.

The control voltage presented to VCO 134 via path 251 is a summation ofseveral voltage sources controlled by microprocesor 202. "Coarse tune"voltage source 230, "fine tune" voltage source 232, "calibrate" voltagesource 234 and "tone" signal voltage source 236 are all summed togetherat summing junction 250 which provides the input voltage to VCO 134.Coarse tune voltage source 230 and fine tune voltage source 232 arecontrolled at separate outputs of a digital to analog converter (DAC)224, output paths 229 and 231 respectively which may be external to andcontrolled by the microprocessor 202 or incorporated withinmicroprocessor 202.

Coarse tune voltage source 230 presents a voltage to the VCO 134,placing the selected signal output from mixer 136 generally in thevicinity of bandpass filter 138. Fine tune voltage source 232 steps involtage steps at 1/5 that of coarse tune voltage source 230 and finetune voltage source 232 is used under control of microprocessor 202 toprovide the sweep voltage at VCO 134. Calibrate voltage source 234provides under control of microprocessor 202 a temperature compensatingvoltage component which is driven via signal path 233 by pulse widthmodulator (PWM) 226. PWM 226 may also be incorporated withinmicroprocessor 202. The tone voltage source 236 may be any tone used forfrequency modulating the output of the VCO 134. A control path 237 isalso provided to tone detector 238 and microprocessor 202 to facilitatetone detection.

The AM detected output from the fine tuning receiver 260 on path 141 isreceived by controller 200 and amplified by an amplifier 240. Asample-and-hold 241 having a microprocessor controlled solid stateswitch is used to sample the detected signal prior to amplification. Theoutput of amplifier 240 is presented at an analog to digital converter(ADC) 228, a level detector 242, and a 60 Hz detector 244. ADC 228provides digital representations of analog inputs. The level detector242 is typically implemented as a comparator circuit and accordingly,sends a signal to microprocessor 202 when a predetermined thresholdlevel has been passed. 60 Mz detector 244 is typically implemented as atone detector circuit, such as that provided by the LM567 chip, theoutput of which sends a signal to microprocessor 202 indicating thepresence of a 60 Hz tone. The detection of the 60 Hz tone is used bymicroprocessor 202 to determine whether to use the 60 Hz linesynchronization sampling mode.

The output signals from FM tone detector 142 on conductor 143 aresampled with sample-and-hold 247, then amplified by an amplifier 246 andpresented to a filter 248 which is a narrow band-pass filter at 10 KHzfor use with the "tone testing" method wherein the tone generated attone voltage source 236 is 10 KHz and the tone detected at tone detector238 is also 10 KHz. The output of filter 248 is presented to tonedetector 238 via signal path 249. The output of tone detector 238 isthen presented to ADC 228 via signal path 239. ADC 228 thus provides atleast two input channels, one for the amplified AM detected signal fromamplifier 240 and one for the output of tone detector 238. Althoughshown as a separate circuit, ADC 228 may also be incorporated withinmicroprocessor 202.

In FIG. 3, the generation of tone voltage source 236 summing junction250 and the tone detection circuitry are shown in more detail. Thesumming junction 250 is implemented by an operational amplifier 302which receives at its inverted input the sum of the signals from coarsetune voltage source 230, fine tune voltage source 232, calibrate voltagesource 234 and tone voltage source 236. The output signals fromamplifier 302 are presented to VCO 134 via conductor 251.

The signal from tone voltage source 236 is presented to summing Junction250 as a triangle waveform, though a pure sinusoid would also work. Togenerate the triangle waveform, a signal from square wave source ispresented to a phase lock loop (PLL) 318 and variable resister 319 whichact as a phase shifter to adjust the phase of the square wave. Theoutput of PLL 318 is presented to integrator 320 which provides atriangle waveform at its output. The tone detector 238 comprises twoparts, namely a synchronous rectifier operational amplifier 304 (alsoknown as a "locking amplifier") and a filter/sample-and-hold implementedwith an operational amplifier 314 and sample-and-hold 315 undermicroprocessor control. The synchronous rectifier output is analog todigital converted at ADC 228.

The synchronous rectifier provided at operational amplifier 304 hasunity gain (+1) when switch 306 is opened and a gain equal to -1 whenswitch 306 is closed. The respective gain from operational amplifier 304is provided by making resistor 310 and resistor 312 equal to one anotherand by making resistor 308 equal to ten times that of resistor 310 or312. The synchronous rectification is controlled at switch 306 by thesquare wave source 316 via control path 237. Phase lock loop (PLL) 318ensures that the rectification timing is aligned with the triangle waveoutput of tone voltage source 236. The PLL 318 is adjusted to producemaximum in-phase output with the tone signal. More particularly, unitygain is provided by the synchronous rectifier when the triangle wave ispositive and -1 gain is provided when the triangle wave is negative.

In one embodiment, the square wave source 316 is provided by a 500 KHzsquare wave source divided by 50 to provide a 10 KHz square wave output.The PLL 318 is implemented with a LM567 tone decoder and used as a phaseadjuster. The integrator 320 may be readily implemented with anoperation amplifier, the design of which is well-known in the art.Similarly, the filter/sample-and-hold configuration implemented byoperational amplifier 314 and sample-and-hold 315 are also well-known inthe art.

The "tone test" is carried out with the above-described tone detectioncircuitry as follows. First, the tone voltage source 236 is enabled bymicroprocessor 202 to provide a 10 KHz tone to summing junction 250. Theoutput of summing junction 250 is then applied to VCO 134 via path 251.In response to the signal on path 251, VCO 134 generates an FM modulatedoutput signal which is mixed in mixer 136 with the signal selected bydetector tuner 130. When the selected signal is mixed with the incominglocal oscillator (e.g., a continuous wave signal from a TV or VCR), anFM modulated 10.7 MHz signal will result when the output of mixer 136 isconverted to that frequency. Using a combination of audio filters and asynchronous tone detector, a local oscillator signal can be reliablydetected even in the presence of significant noise, since noise will notproduce a tone and hence will not produce an output from the synchronousrectifier.

An FM discriminator or slope detection on the steep crystal skirt can beused to detect the 10.7 MHz intermediate frequency signal. In analternative embodiment of the tuned channel detection apparatus, the10.7 MHz crystal filter design was eliminated by using a doubleconversion frequency shift keying (FSK) chip where filtering could bedone at 455 KHz using inexpensive ceramic filters. In addition, asshould be appreciated by those skilled in the art, the tone injectionmethod of discerning a low level continuous wave signal is not limitedto a particular application, and thus may be useful to detect any lowlevel continuous wave signal, not just local oscillator signals.

When the synchronous rectifier output of the operational amplifier 304of tone detector 238 is synchronized with the tone voltage source 236,the amplified and filtered signal appearing at the input to thesynchronous rectifier from filter 248 is a distorted sine wave plusnoise if a local oscillator signal to be detected is present.Alternatively, when no local oscillator signal is present, only noisewill be presented from the output of filter 248. When the fundamental ofthe distorted sine wave signal is in phase with the synchronousrectifier, the result at signal path 313 will be a full wave rectifiedsignal. This occurs because when the incoming sine wave goes positiveduring one-half the cycle, the gain is +1 resulting in a positive goinghalf cycle and during the second half cycle the sine wave goes negativebut the gain is also -1 resulting in another positive half cycle, hencea full wave rectified output is produced. Note that any noise, eventhough it may be significantly larger than the continuous wave signal,will not result in rectification since it is random in phase andfrequency relative to the operation of the synchronous rectifieroperation of operational amplifier 304.

FIG. 4 shows an embodiment of the fine tuning receiver 260. Asillustrated, all functions of the fine tuning receiver 260 areimplemented by a single FSK receiver chip 401. In the embodiment of FIG.4, the FSK receiver chip 401 is a Motorola MC3356 data receiver whichincludes a front-end mixer/local oscillator. Tuning of the VCO 134frequency is provided from the voltage at summing junction 250 which isapplied to varactor diode 402. The resultant capacitance changes ofvaractor diode 402 affect a tank circuit implemented with capacitor 403,capacitor 405, and inductor 404, which controls the oscillator outputfrequency. The 10.7 MHz filter is implemented with crystal 406. Theresulting 10.7 MHz bandpass filter has a 15 KHz bandwidth. Asimplemented, the VCO 134 is provided by varactor 402 wherein the localoscillator may be tuned over a narrow range (approximately 500 KHz). Asecond varactor (not shown) may be used for additional temperaturecalibration. FM detection as implemented by the MC3356 chip is based onusing slope detection via the steep skirt of the 10.7 MHz crystal.

FIG. 5B shows the results of tuning the TV 102 to channel 30 while thereflections for channels 23 through 37 were measured. Of course, inactual operation a complete table for all channels on the system wouldbe generated for use by the tuned channel apparatus. Then, by looking ateach channel under test starting at channel 25 and comparing the channelsignal plus the two adjacent upper and lower channel signals with theknown "attributes" (FIG. 5A), the controller 200 generates an "error"table as illustrated in FIG. 5C.

As an example of such "attributes", assume channel 25 is being tested.If channel 25 were the correct channel for reflections for the carriersfor channels 23, 24, 25, 26 and 27 should be -10, -10, -16, -16 and -8respectively (see FIG. 5A). However in the instant example, the actualmeasurements were -7, -5.5, -4, -6.5 and -8.5 respectively (see FIG.5B). The resulting errors: 3, 4.5, 12, 9.5 and -0.5 are tabulated inFIG. 5C. By comparing the errors, the controller 200 can calculate a"figure of merit" by summing the absolute values of all the errors. Asillustrated in FIG. 5C, Fm3 sums the "test" channel plus each adjacentsignal (3 values) and Fm5 uses two adjacent signals (5 values).Alternative "figure of merit" computations could be used for Fm7 or Fm9and so on. These are very simple arithmetic operations and can be donerelatively quickly by the controller 200, once tabular data such asillustrated in FIG. 5B is generated.

The controller 200 then looks to FIG. 5C and scans the Fm3 or Fm5columns for the lowest figure of merit, the tuned channel is clearlychannel 30 which is the correct channel. Note however, that the bestreturned loss occurs on channel 31 not channel 30 in FIG. 5B. This isnot uncommon and it illustrates that using adjacent signals improves theaccuracy of the return loss method.

The return loss method may be used by itself or in conjunction with anlocal oscillator detection method. Each of these methods vary in speedand accuracy depending upon the particular signal and conditions. Thus,artificial intelligence techniques have been found useful in determiningwhich method to use for particular signals.

Certain channels are sent in a scrambled mode. When the local oscillatorto be detected lies within the spectrum of an interfering scrambledchannel, the vertical synchronization interval may not be detected fromthe scrambled signal because a common technique for scrambling a channelis to suppress the synchronization interval information. Thesynchronization interval information could be recovered by each channeldetection arrangement, however, providing such will add to the systemcost. Circuitry for communication of such information over a cable suchas data path 204 provides a less expensive solution, the circuitryextracts the synchronization interval information at the "head end" viaa de-scrambler converter controlled by the central control computer 206.The synchronizing information for scrambled channels is then conveyed tothe individual channel detector units over the data path 204.

FIG. 6A represents circuitry at the head end associated with centralcontrol computer 206, and FIG. 6B represents circuitry used by themicroprocessor 202 at the remote detector. A precision 60 Hz clocksignal is derived from a crystal oscillator 602 at the head end. Each ofthe remote channel detectors generates clock signals which aresynchronized or "locked" to the central clock signals using a standardphase-lock loop (PLL) circuit 606. The PLL 606 compares a "reference"frequency from a VCO 608 with synchronizing information from the datapath 204 and then derives a frequency using digital counter 610. Thephase relationship of the two frequencies is analyzed, resulting in acorrection voltage that tunes the VCO 608 such that the frequencies atthe head end and in the channel detector "lock" in both frequency andphase. The "reference" can be broadcast over data path 204 or over aseparate data channel to all remotes. There will, of course, be atransport delay, but this same delay also applies to the TV signals soproper synchronization is maintained.

At the central control computer 206, composite video signal is detectedwith a converter de-scrambler 618. Vertical synchronization intervalinformation is then extracted from the scrambled signal withsynchronization interval detector 620. A flip-flop 622 triggers a 1.2millisecond pulse from one-shot monostable 624 corresponding to eachvertical synchronization period. The 1.2 millisecond pulse interruptsthe central control computer 206 and latches the current clock count ofa counter 612 in a latch 614. The central control computer 206periodically tunes to each scrambled channel, establishes a "time stamp"relative to its clock (and hence the remote clocks), adds a "correction"input value to compensate for any communications protocol delay in orderto maintain constant delays, and finally transmits this information tothe microprocessors 202 at the remotes. Since there will be a slow"drift" input error, an updated "time stamp" input should be sentperiodically, typically every five to ten seconds. The update period canbe extended significantly if the central control computer 206 calculatesthe "drift rate" for each channel and transmits this information to theremotes, thus allowing the microprocessor 202 to compensate for thedrift at the remote units.

At the remote units, as illustrated in FIG. 6B, a closed loop maintainsthe phase relationship between the central control computer 206 and theremote units, wherein PLL circuit 606 drives VCO 608, which drivescounter 610 which, in turn, closes the loop to PLL circuit 606. Logiccompare 626 conveys phase information to microprocessor 202 via 8-bitregister 628. The VCO 608 output is ANDED with the logic compare 626 atAND 630, which, in turn, provides an interrupt signal to themicroprocessor 202 and generates a 1.2 millisecond verticalsynchronization interval pulse at the remote unit, with one-shotmonostable 632, thus providing vertical synchronization intervalinformation for the scrambled channel which was decoded at the centralcomputer 206 and which is now in synchronization interval with thesynchronization interval pulses generated for sampling at the remotetuned channel detector units.

Another approach for conveying the synchronizing information withrespect to scrambled channels would use a reference channel (e.g.,channel #6), and then have the head end broadcast reference time shifts(±Δ) and drift rate relating the reference channel to the scrambledchannel synchronizing information for use at each remote unit from timeto time as required. This reference channel approach avoids additionalphase lock circuitry.

The preceding embodiment involves a tuned channel detector connecteddirectly to the RF input of a TV 102 and uses a detector tuner 130capable of detecting local oscillator signals generated by a televisionreceiver. When a set top converter is inserted between the TV 102 andthe tuned channel detector, it is the local oscillator of the set topconverter which must be analyzed to identify a tuned channel.

FIG. 7 shows an alternative signal selection module 700 for use as asubstitute for signal selection module 104 when a set top converter (notshown) is connected to input path 110 before TV 102. Selection module700 separates the local oscillator signals from the set top converter,ranging from about 668 MHz to about 1258 MHz, and converts them tofrequencies selectable by detector tuner 130.

When a set top converter is used, directional coupler 120 may bereplaced by a 600 MHz crossover network 702 (a diplex filter), becausethe TV carrier signals are below 600 MHz while the local oscillatorsignals leaking back from the set top converter are over 600 MHz. Thecrossover network 702 passes television carrier signals right to leftfrom communication path 114 to path 110. The crossover network 702 alsopasses the leaked local oscillator signals which exceed 600 MHz from thecommunication path 110 to a block converter 704. The block converter 704converts the local oscillator signals from the set top converter by apreset amount down to a frequency which may be received at detectortuner 130. It should be mentioned that block converter 704 may beavoided if a detector tuner 130 is used which is capable of receivingthe higher local oscillator signals from the set top converter.

FIG. 8 is a detailed schematic diagram implementing the alternativesignal selection module shown in FIG. 7 for use with a tuned channeldetector when a set top converter is used by the viewer.

With a table-driven software embodiment, the controller 200 accumulatestest instructions and apparatus parameters on a per channel basis usingtables having such information. The per channel tables represent asegregated database wherein channel specific testing modes are defined.The controller 200 reads each per channel table in sequence; performsthe called-for tuned signal testing; determines whether the current perchannel corresponds to the tuned channel; then reads the next perchannel if the tuned channel has not yet been located. In this way, thecontroller 200 proceeds through the database of per channel tables untilsatisfied that the correct channel has been identified. When thecontroller 200 detects that the channel has been changed at TV 102, thenthe process is repeated until the new tuned channel is determined by thecontroller 200.

As an example of the way in which the parameters contained in the perchannel tables are used within the table-driven software, channel testdata associated with the detection process are contained in sets of perchannel tables each having an identical format--one for each channel,corresponding typically to the format shown in TABLE 1 below. Theparameters in TABLE 1 are initialized to predetermined values. Exceptfor the tuner values, initial values are the same for all channels. Thechannel numbers start at entry 02 and go to 108. Within each table areentries which contain specific control parameters for the particularchannel.

The following TABLE 1 represents a per channel table entry format fordemonstrating the preloading of values used at each tuned channeldetector for controlling table-driven software:

                  TABLE 1    ______________________________________    ENTRY   PARAMETER    ______________________________________     *1     ENABLE       Channel enable byte:                         00 = SKIP this chan.                         01 = TEST this chan.                         10 = END of seq.; re-start                         at 1st chan.     2      RL ENABLE    Return loss test enable                         byte:                         00 = NO (Local oscillator                         test this chan.)                         11 = YES (Return loss test                         this chan.)     3      channel #    Channel to be tested     4      tuner1       Tuner control #1 to tune to the                         picture carrier of the channel                         in which the local oscillator                         lies in order to pick up the                         interfering channel's vertical                         synchronization interval when in                         sample mode.     *5     ifctune1     IF coarse tune     6      ifftune1     IF fine tune     7      rfgain1      RF gain     8      ifgain1      IF gain     9      tuner2       Tuner control #2 used to tune to                         the local oscillator for this                         channel.    *10     ifctune2     IF coarse tune     11     ifftune2     IF fine tune     12     rfgain 2     RF gain    *13     ifgain 2     IF gain    *14     HIT level    Initial "hit level" setting                         represents a 2 volt threshold                         (adjustable).    *15     HIT dev      The deviation above the hit                         level in which the local                         oscillator must lie to be a                         "hit".     16     sample de    Delay between samples    *17     samples      Samples per vertical sync. (or                         60 Hz sync.)     18     TONE MODE    Tone test    *19     relay        Determines state of relay A/B                         switch during sync. detect                         cycle.    *20     SEL 60 HZ    Bypasses the vertical                         synchronization interval detect                         cycle and uses the 60 Hz line                         for sync.    ______________________________________     *denotes parameters which may need to be changed for a particular channel     The other entries typically are not usually changed.

The above TABLE 1 is intended for use with software represented by theprogram flow chart shown in FIG. 9 (described below), which implementsthe table-driven software scheme using programmable channel detectiontable entries for channel detection data and parameters for determiningthe tuned channel.

The parameters set up the detector configuration for measurements at thechannel associated with the parameters. Once the detector is configuredaccording to the table parameters, measurements are then made by thechannel detector for local oscillator signals and/or for TV channelcarrier signals at the various frequencies which are being considered.In addition, each table entry provides information specific to thechannel under consideration. More particularly, information relating tothe best method of tuned channel detection for the particular channel,the "hit level," and "hit deviation" are stored for use by thetable-driven software.

Many of the table parameters are preloaded and usually do not need to bechanged. Some parameters, however, will need to be adjusted dependingupon the local oscillator frequency, signal level and/or signal-to-noiselevel. Such adjustments are facilitated through the training software.Channel parameter entries having an asterisk(*) denote the parameterswhich may require some adjustment. As the program associated withcontroller 200 proceeds in accordance with the table-driven softwarescheme, the parameters associated with each channel are used bycontroller 200 in determining how to proceed with its testing.

To look for the local oscillator for the TV 102, the controller 200scans through all the channel table entries for a "match," displays thechannel number on numeric display 220, lights a green light at the lamps222, and logs the appropriate channel number either in a data structureassociated with microprocessor 202, or to terminal 218, or to thecentral control computer 206 via the data path 204. The detectorcontinues to monitor the local oscillator signal until it disappears, atwhich time the detector turns off the green light at the lamps 222 andthen seeks out the next tuned channel.

The enable parameter tells the controller 200 whether to skip theparticular channel associated with the table, or whether to test thechannel, or whether the detector has reached the end of the testsequence and should restart the loop (usually at channel 2). The returnloss enable parameter tells the detector whether to use return loss orlocal oscillator testing for channel detection. By using a program tocall up all of the channel table entries in sequential order, thecontroller 200 merely loops through all of the candidate channels, teststhem, and logs them accordingly.

The channel # parameter represents the channel number (2-108) associatedwith the particular channel table entry. The tunerl parameters are usedto tune the picture carrier of the interfering channel in which thelocal oscillator lies in order to pick up the channel's verticalsynchronization interval when using the vertical synchronizationinterval sampling, or to tune in the picture carrier signals for thereturn loss mode of testing. The next parameters relate to the IF coarsetune, IF fine tune, RF gain, and IF gain, associated with the tunerlconfiguration. Then, tuner2 is used to tune the local oscillator for theparticular channel under test. The next four parameters relate toparameters associated with IF coarse tune, IF fine tune, mixer RF gain,and mixer IF gain for the tuner2 configuration.

The remaining parameters in the channel table relate to the criteria fordetermining the tuned channel and the particular testing method. The"hit level" parameter represents an initial setting of 2 volts as thethreshold for determining the presence of the local oscillator signal.The "hit level" may be changed to be more or less than 2 volts. The "hitdeviation" parameter represents the deviation above the hit level inwhich the local oscillator signal must lie in order to be considered tobe a "hit." The next parameter determines the delay between samplingwhen the sample mode of testing is used, and the parameter after thatrelates to the number of samples per vertical synchronization intervalor 60 Hz sync. The "tone mode" parameter instructs the tuned channeldetector to use the tone method of testing for the particular channelassociated with the table. The "relay" parameter determines the state ofthe switch 124 during the vertical synchronization interval detect cycleassociated with detecting the vertical synchronization interval and thegeneration of the "pseudo-sync" referred to above. Finally, the "elect60 Hz" bypasses the vertical synchronization interval detect cycle anduses the 60 Hz line for synchronization during the sampling mode oftesting. This may be done to stabilize the picture carrier signalmeasurement.

The program flow chart of FIG. 9 further illustrates the table-drivensoftware. The controller 200 uses the above-described table entries sothe program flow chart shown generally at 900 is able to detect thetuned channel. The program flow starts at the FIRST TABLE 902, at whichpoint the controller 200 reads the table associated with the firstchannel to be tested and its associated parameters to configure thetuned channel detector and then proceeds accordingly. Typically thefirst channel will be channel 2, however it has been found advantageousto configure a channel table entry 01 chosen as a thermal compensationchannel for running recalibration routines since there usually is not achannel 1. The tuner values in the table are not actually for channel 1however, rather any channel which is good for making thermalcompensation adjustments will suffice (in one embodiment channel 7 wasused).

Next ENABLE 902 checks for one of three table entries: skip, test, orend. End causes the microprocessor 202 to re-start at FIRST TABLE 902.Skip causes the controller 200 to proceed to NEXT TABLE 906 whichincrements an index to the next table. Test causes the microprocessor202 to proceed with testing for the channel associated with the presenttable. SAMPLE 908 determines whether or not a sample mode of testing isto be employed. If a sampling mode is to be used, SEL₋₋ 60 910determines whether 60 Hz sampling should be used. V-SYNC 912 configuresthe detector apparatus for vertical synchronization interval sampling if60 Hz sampling is not used, otherwise 60₋₋ HZ 914 configures theapparatus for 60 Hz sampling. RL₋₋ ENABLE 916 determined whether returnloss testing is to be used, and if not TONE₋₋ MODE 918 determineswhether tone testing for local oscillator is to be used.

The actual testing for tuned channel detection is carried out at RL₋₋TEST 920, TONE₋₋ TEST 924, and LO₋₋ TEST 928. When a tuned channel isdetected with one test, it may be verified with another test to ensureproper detection. Channel hits are detected at RL₋₋ HIT 922, TONE₋₋ HIT926, and LO₋₋ HIT 930. As can be seen from the program flow chart 900,once a tuned channel is detected, the channel is repeatedly tested untilthe channel changes at which time the next table is selected and theabove-described program loop is then repeated. The describedtable-driven software scheme is merely a simplified and basic example ofthe way in which tuned channel detection is implemented; numerousmodifications and enhancements should be readily apparent to thoseskilled in the art.

In particular, an alternative "mixed mode" of tuned channel detectionhas been found useful as an adjunct to regular local oscillator testing.In this mode, selected channels are singled out for return loss testing.All other channels will be local oscillator tested. One reason for doingthis is that for particular channels the local oscillator signal may betoo low to be detected reliably, or there may be an extraneous signalthat could be confused for an local oscillator signal. In the mixedmode, selected channels are individually return loss tested as scanningoccurs. As already discussed, another alternative is to use the varioustypes of testing as checks against one another to ensure accuratedetection. Basically, the program flow illustrated in FIG. 9 is merely acore upon which higher level programs used by the controller 200 canbuild in order to develop more sophisticated testing schemes.

In conjunction with the table-driven software and artificialintelligence techniques referred to above, the tuned channel detectorsystem undergoes a process of "system training." Training is defined asthat process by which the system "learns" the attributes of the TV 102operating in a specific environment. This can be done manually for eachdetector system or through a process of self-training which usesartificial intelligence programming techniques in software.

Manual training involves stepping the TV 102 through each of the activechannels. The detector system logs into the controller 200 all theattributes for each channel. These attributes will then be used duringthe "run" mode to identify which channel is being tuned. The softwarefor this is relatively straightforward.

Self-training involves artificial intelligence techniques whereby thecontroller 200 starts with certain assumptions, then adds to itsknowledge through trial and error. The disadvantage of self-training isthat its error rate tends to be quite high initially and improves withtime. The software must keep track of various trend data. Another typeof self-training that can significantly improve detect time is to builda "profile" of the viewer's habits. Most viewers have quite definiteviewing habits or patterns. Such viewing patterns can be exploited bytesting for the viewer's most likely channels first. Some of theattributes stored for each channel would thus include: which channelsare active on the system; the reflection coefficient for each signal;the local oscillator frequency and amplitude for each signal; andwhether local oscillator amplitude, tone, or sampling mode detection ispreferable.

One should keep in mind that either the return loss or local oscillatormethods of testing may be used to determine the channels to which the TV102 is tuned, or some combination of the methods may also be used toensure accurate detection. Unless the local oscillator signal isextremely low or buried in noise, local oscillator testing is generallyfaster than return loss testing, because often the picture carriers usedfor return loss measurements have to be sampled only during the verticalretrace interval, when the carriers are fairly constant (no picturecontent). Also, either vertical synchronization interval sampling orline synchronization sampling may be used with the amplitude or tonelocal oscillator methods, and such sampling may also be used with thereturn loss method as well. Artificial intelligence techniques may alsobe used to exploit optimal detection methods based upon particulartesting conditions and adversities.

While there has been described the preferred embodiments of the presentinvention, numerous modifications and changes will naturally be apparentto those skilled in the art. It is therefore intended by the appendedclaims to define all such modifications and changes as fall within thespirit and scope of the invention.

What is claimed is:
 1. A continuous wave detection apparatus fordetecting the presence of a low level continuous waveform amplitudewithin an input signal comprising the low level continuous waveform andan interfering signal, said apparatus comprising:a source of a firstperiodic signal; means for frequency modulating said first periodicsignal with a second periodic signal producing a frequency modulatedsignal; means for frequency shifting the input signal by a frequencycorresponding to the frequency modulated signal; filtering means forselecting a signal within a predetermined range of frequencies from thefrequency shifted input signal; and means for detecting said secondperiodic signal in the signal selected by said filtering means toidentify the presence of said low level continuous waveform therein. 2.The apparatus of claim 1, wherein said means for frequency shiftingcomprises means for shifting the input signal by a sweep of frequencies.3. The apparatus of claim 1 wherein said second periodic signalcomprises a periodic triangular waveform.
 4. The apparatus of claim 1,wherein the detecting means comprises a synchronous rectifiersynchronized with said second periodic signal; and wherein the apparatuscomprises means for integrating a rectification timing signal of saidsynchronous rectifier to generate said second periodic signal.
 5. Theapparatus of claim 4 wherein the apparatus comprises controller meansfor comparing the signal output from said synchronous rectifier to apredetermined signal threshold to discern the presence of said low levelcontinuous waveform.
 6. A tuned signal detection apparatus for use witha television receiver tuned by a local oscillator signal to a tuned oneof a plurality of incoming television signals demarcated by verticalsynchronization intervals; said local oscillator signal having adifferent predetermined frequency for tuning said receiver to differentones of said incoming television signals, said tuned signal detectionapparatus comprising:means for receiving a signal representing the localoscillator signal generated by said receiver; means for selecting anindividual one of said incoming television signals; means for detectingthe vertical synchronization intervals for the selected incomingtelevision signal; and controller means responsive to said detectingmeans for measuring, only during the vertical synchronization intervalsfrom the selected incoming television signal, the local oscillatorsignal generated by said receiver for tuning the tuned one of theplurality of incoming television signals.
 7. The apparatus of claim 6,wherein said selecting means comprises controller means for identifyingan individual one of said incoming television signals interfering withsaid local oscillator signal, and controller means for selecting saidtelevision signal interfering with said local oscillator signal.
 8. Atuned signal detection apparatus for use with a television receiver fortuning to one of a plurality of television signals, the televisionreceiver generating local oscillator signals having a differentpredetermined frequency for tuning said receiver to each of saidplurality of television signals, the local oscillator signals beingmodulated by a 60 Hertz power line signal, said tuned signal detectionapparatus comprising:means for detecting a synchronized sampling pointin 60 Hertz power line modulation cycles; and controller meansresponsive to said detecting means for identifying the presence of oneof the local oscillator signals having a frequency for tuning saidreceiver to a particular one of said plurality of television signals,only during the synchronized sampling point in 60 Hertz power linemodulation cycles.
 9. A tuned signal detection system for detecting oneof a plurality of television signals to which a television tuner istuned, said plurality of television signals comprising a scrambledtelevision signal, said detection system comprising:means at a locationremote from said television tuner for receiving said plurality oftelevision signals and for measuring vertical synchronization timingintervals from the scrambled television signal thereof; means forsending a synchronizing signal identifying said measured timingintervals from said remote location to a tuned signal detection devicelocal to said television tuner; and means, at said tuned signaldetection device, responsive to said synchronizing signal for detectingone of a plurality of television signals in synchronism with said timingintervals measured at said remote location.